The present invention generally relates to catalyst composites containing extruded catalyst supports, and methods of making and employing the catalyst composites. The present invention particularly relates to catalyst materials and methods associated with the purification of terephthalic acid.
Catalytic processes are indispensable in the chemical industry. Frequently, catalytic processes employ a catalyst that is incorporated on a support. Effective use of the catalyst often corresponds to the quality of the catalyst support. Poor quality catalyst supports, due to at least one of physical degradation, chemical degradation, undesirable properties, and inconsistent properties, limit the effectiveness of catalysts incorporated therein. Conditions such as high temperatures, high pressures, and high or low pH environments present challenges to the integrity of catalyst supports.
For example, conventional catalyst composites for the purification of terephthalic acid by the Amoco mid-continent process (PTA catalysts) are composed of palladium-supported on granular 4xc3x978 mesh carbon. These catalyst composites are designed to remove the two major impurities present in crude terephtahlic acid; namely yellow color and 4-carboxy benzaldehyde (4-CBA).
Carbon is the preferred support material for conventional PTA catalysts because it is essentially the only readily available material that can simultaneously yield an effective catalyst for color removal, 4-carboxy benzaldehyde removal, and also withstand the extremely corrosive environment of the terephthalic acid purification process. Although conventional carbon supported PTA catalysts have been used extensively over the past 20 years, such catalyst composites suffer from several disadvantages. These disadvantages include: highly irregular shapes leading to possible mal-distribution of liquid or gas flows in a catalytic reactor bed utilizing such catalyst composites; irregular shapes having sharp and fragile edges and corners which tend to break off and contaminate the PTA product with undesirable dust and black particles; brittleness which also leads to breakage and dust/black particles contaminating the PTA product; natural origin, i.e., coconut shell, which leads to non-uniformity form one growing season to another and consequent non-consistency of the carbon support; and being commonly derived from nutshells, such activated carbon is highly microporous, leading to the requirement of locating all of the active catalytic metal at the surface of the particles, where it is undesirably susceptible to loss during the movement and abrasion which occurs during shipping and handling.
Particularly problematic is the unpredictable and uncontrollable melange of irregular shapes and sizes associated with commonly employed granular cocoanut carbon supports. Granular cocoanut carbons are also mostly microporous; that is, they have numerous pores having a pore diameter less than 50 xc3x85. As a result, the catalytic metals must be located near the exterior edges of the supports to avoid low activity due to mass transfer resistances. However, when catalytic metals are located near the exterior edges of supports, they are subject to loss due to mechanical attrition and thus the catalyst support loses its activity. Catalytic metals located near the exterior edges of a support are readily accessible to corrosion metals commonly present in reactor feeds and thus subject to deactivation.
Non-carbon catalyst supports are employed in catalytic processes in attempts to overcome the disadvantages associated with conventional carbon supported catalysts. Non-carbon supports include alumina supports, silica supports, alumina-silica supports, various clay supports, titania, and zirconium supports. However, there are at least one of two disadvantages associated with non-carbon catalyst supports; namely, that they may become weak and loose physical strength, that they are dissolved in highly corrosive environments (such as hot aqueous solutions of terephthalic acid) and that they have difficulties in removing undesirable color from crude terephthalic acid.
Improved catalyst supports and catalyst composites are therefore desired. Specifically, improved PTA catalyst supports and PTA catalyst composites are desired to provide improved methods of purifying terephthalic acid and improved useful lifetimes.
The present invention is designed to address at least one of and preferably all of the above disadvantages by providing a catalyst composite containing a composite support which is formed into shapes with mesoporosity and macroporosity. The catalyst composites of the present invention enjoy an extended useful lifetime compared to conventional catalyst composites since they contain a support composed of an extruded carbonaceous material capable of withstanding harsh, corrosive reaction environments, such as those encountered in PTA catalysis. In this connection, the catalyst composites of the present invention have a lower deactivation rate than conventional catalyst composites. The catalyst composites of the present invention also enjoy the same or better activity with about 30% to about 50% by weight less active metal compared to conventional catalyst composites.
One aspect of the invention relates to a catalyst composite containing a metal catalyst and an extruded catalyst support containing an extruded activated carbonaceous material having specifically a defined pore structure. For example, the extruded activated carbonaceous material may have pores wherein at least about 40% of total Hg porosity occurs in pores having a diameter of about 200 xc3x85 or larger. Alternatively the extruded activated carbonaceous material may have a first set of pores having a pore diameter of at least about 40 xc3x85 and at most about 100 xc3x85 with a porosity of at least about 0.15 cc/g, and a second set of pores having a pore diameter of at least about 5,000 xc3x85 and at most about 20,000 xc3x85 with a porosity of at least about 0.3 cc/g.
Another aspect of the invention relates to a method of making a catalyst composite involving mixing at least one carbonaceous material and a liquid to form a mixture; extruding the mixture into a shaped material; optionally drying the shaped material; heat treating the shaped material at a temperature from about 600xc2x0 C. to about 1,500xc2x0 C. to provide a catalyst support, wherein the catalyst support has at least one of the two to four specifically a defined pore structures, and contacting a precious metal catalyst with the catalyst support.
Yet another aspect of the invention relates to a method of purifying a crude polycarboxylic aromatic acid composition involving contacting the crude polycarboxylic aromatic acid composition with a catalyst composite containing a metal catalyst and an extruded activated carbonaceous material having at least one of the two to four specifically a defined pore structures. And still yet another aspect of the invention relates to a method of purifying a crude amine composition or a crude alkynol amine composition involving contacting the crude amine composition or the crude alkynol amine composition with a catalyst composite containing a catalyst support containing a metal catalyst and an extruded activated carbonaceous material having at least one of the two to four specifically a defined pore structures.